Hydroelectric power plants (e.g. in rivers and dams) use turbines to convert the kinetic energy of water into electrical energy.

The advantage that hydroelectric power offers over wind and solar energy is that the process of electricity generation can be controlled more easily in line with how much electricity is needed at any given time. High-lying water reservoirs can also serve as energy storage. If an electricity surplus exists, water is pumped up to a higher level. When electricity is needed, water is allowed to flow down to a lower level and is conducted through a turbine. These features are very beneficial to the stability of electricity supply in the system as a whole.

The cost of investing in hydroelectric power plants can be redeemed after just a few years. At existing sites, it is often worth considering an upgrade and increasing the capacity of the turbines by means of repowering. As with wind energy, hydroelectric power plants have a relatively high minimum output. They are therefore best suited for large-scale applications. However, suitable solutions are available for smaller requirements also.

Globally, over 1,240 gigawatts of hydroelectric capacity were installed in 2016 (see IRENA).

German companies have been involved in developing, building and operating hydroelectric power plants for more than 100 years. Globally, at least half of all hydroelectric power plants are based on German technology.

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Since the space and locations for large-scale hydropower plants are limited due to the geographical and environmental conditions required, growth rates for this technology lag behind solar or wind energy.

There are three main types of large-scale hydro power plants: run-of-the-river plants, pumped storage plants and storage plants. Run-ofthe- river plants are constructed in large rivers with high flow volumes, while pumped storage and storage plants require a height slope and are most often located in mountain ranges or river valleys.

Small hydropower plants are often situated on small rivers and can have water basins of different sizes and types of construction. Micro and mini hydropower plants can be
differentiated based on their capacities as follows.

Several types of turbines can be used to generatehydropower. Choosing the most suitable type of turbine depends on the rate of flow, the drop height and the pressure of the water driving the turbine.

Francis turbines: The Francis turbine is one of the oldest and most commonly used conventional turbines. It is suitable for a wide spectrum of flow rates and drop heights of 20 to 700 m. However, it operates best when water volumes are steady.

Kaplan and bulb turbines: Kaplan and bulb turbines are suitable for small drop heights and a wide range of fluctuating water volumes, which makes them ideal for large run-of-the-river hydropower plants.

Pelton turbine: Pelton turbines are impulse-type turbines used for drop heights of 100 up to 1,500 m and low water volumes. They are highly suitable for pumped storage power plants.

Hydrodynamic screws: Other types of turbines include hydrodynamic screws, which work on the principle of Archimedes’ screw and are primarily used for low drop heights and low capacities. Cross-flow turbines: Cross-flow turbines are used for low drop heights and low water volumes. They generally have a small capacity.